The present invention relates to a DC-to-AC power inverter and a method of operation for the DC-to-AC power inverter, and more particular to those applied to DC-to-AC power inverters.
DC-to-AC power inverters are commonly used in equipment such as uninterruptible power supplies (UPSs), motor drives, and other applications. Conventional DC-to-AC power inverters use a pulse width modulated technique to stabilize the output voltage thereof. Please refer to FIG. 1 which is a schematic diagram illustrating a DC-to-AC power inverter according to the prior art. As shown FIG. 1, the DC-to-AC power inverter 100 includes a switching circuit 101, a RMS voltage calculation module 102, a summing module 103, a voltage control module 104, a phase lock loop 105, a multiplier module 106, and a voltage mode control circuit 107. Meanwhile, the voltage mode control circuit 107 operates the switching circuit 101 as a voltage controlled inverter. The voltage mode controller 108 is here shown as including a plurality of modules executing on a combination of a data processor (e.g., a microprocessor, digital signal processor (DSP), or combination thereof) and an associated memory. The modules include the RMS voltage calculation module 102 that computes an RMS voltage Vrms from an output voltage Vout sensed at the output port 109. The RMS voltage Vrms is subtracted from a first reference voltage signal Vref1 at a summing module 103 to determine a second reference voltage signal Vref2. The second reference voltage signal Vref2 is modulated by the voltage control module 104 to generate a third reference voltage signal Vref3. The reference signal xcex8 is processed by the phase lock loop 105 and multiplied by the third reference voltage signal Vref3 in the multiplier module 106 to produce a computed reference voltage signal Vref. Hence the voltage mode control circuit 107 responsive to the reference voltage signal Vref and the output voltage Vout operates the switching circuit 101 as a voltage controlled inverter.
Generally speaking, there are some drawbacks in the typical parallel operation of an uninterruptible power supply system to be described as follows:
(1) Computationally intensive operations, such as RMS voltage calculations, need a complex circuit or expensive circuit, such as the DSP chip to implement the calculation.
(2) On the other hand, the DC-to-AC power inverter needs a multiplier module to perform the voltage command signal calculation. It will exhaust a great amount of hardware resources to perform the voltage command signal calculation, whether it is implemented by digital signal processing architectures or corresponding analog signal processing architectures.
It is therefore attempted by the applicant to deal with the above situation encountered with the prior art.
It is therefore an object of the present invention to propose a DC-to-AC power inverter and a method of operation for the DC-to-AC power inverter to reduce computationally intensive operations, such as RMS voltage calculations and multiplication calculations.
According to an aspect of the present invention, a DC-to-AC power inverter includes an input port, an output port, a switching circuit electrically connected between the input port and the output port responsive to control signals to convert a DC voltage at the input port to an AC output voltage, and a system controller for sensing the AC output voltage at the output port and transforming the AC output voltage to generate a first reference current signal, for sensing an output current at the output port to generate an output current signal, for generating a reference current signal by adding the first reference current signal to the output current signal, and for generating the control signals responsive to the reference current signal and a sensed inverter current signal by sensing an inverter current at the switching circuit.
Preferably, the system controller includes a inverter current sensor coupled to the switching circuit for sensing the inverter current at the switching circuit to generate the inverter current signal, an output current sensor for sensing the output current at the output port to generate the output current signal, a voltage control circuit coupled to the output port and the output current sensor for generating the reference current signal responsive to the output current signal and the sensed output voltage signal, and a current mode control circuit coupled to the voltage control circuit to generate the control signals responsive to the first reference current signal.
Preferably, the voltage control circuit includes a voltage sensor coupled to the output port for sensing the AC output voltage to generate the output voltage signal, a subtractor received the output voltage signal and a reference voltage signal for generating an error voltage signal by subtracting the output voltage signal from the reference voltage signal, a voltage controller coupled to the subtractor for transforming the error voltage signal to the first reference current signal, and an adder coupled to the voltage controller and the output current sensor for generating the reference current signal responsive to the first reference current signal and the output current signal.
According to another aspect of the present invention, a control method for a DC-to-AC power inverter, wherein the DC-to-AC power inverter comprises an input port, an output port, a switching circuit electrically connected between the input port and the output port responsive to control signals to convert a DC voltage at the input port to an AC output voltage, includes the steps of sensing the AC output voltage at the output port and transforming the AC output voltage to generate a first reference current signal, sensing an output current at the output port to generate an output current signal, generating a reference current signal by adding the first reference current signal to the output current signal, and generating the control signals responsive to the reference current signal and a sensed inverter current signal by sensing an inverter current at the switching circuit.
Preferably, the control method further includes the steps of sensing the inverter current at the switching circuit to generate the inverter current signal, sensing the output current at the output port to generate the output current signal, generating the first reference current signal responsive to the output current signal and the sensed output voltage signal, and generating the control signals responsive to the first reference current signal.
Preferably, the control method further includes the steps of sensing the AC output voltage to generate the output voltage signal, generating an error voltage signal by subtracting the output voltage signal from the reference voltage signal, transforming the error voltage signal to the first reference current signal, and generating the reference current signal responsive to the first reference current signal and the output current signal.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: